1. Field of the Invention
The present invention relates to a rolling member guiding structure, and more particularly, to a guiding structure to be used to stabilize the moving direction of a sliding block so as to cause the rolling member to be able to circulate smoothly in a linear transmission mechanism for use in the tool machine or the automatic manufacturing machine, used in the electronic and semiconductor industry.
2. Description of the Prior Art
In a conventional linear transmission mechanism, its rolling member is composed of a plurality of rolling balls and spacers, and a connecting chain for the spacers. Therefore, the cyclic guiding structure should be configured to match the profile of the rolling member and it is designed in three types. The first type is integrally formed in one piece such as one disclosed by U.S. Pat. No. 5755516, but the injection molding process is applied due to its complicated structure. The existing problems to be solved include the following.
The strict allowable dimensional deviation existing between the size of the cyclic guiding structure and the sliding block make it difficult to control the shrinking fit for the guiding structure.
Secondly, high fabrication technique is required to overcome the difficulty in forming a hollow circulation tunnel in an internal circulation guide structure so as to allow the rolling member to circulate stably therein.
In addition, such a structure needs a considerably broad contact area between the rolling member and the circulation tunnel that results in a large frictional force and greatly retards the motion of the rolling member.
A typical two piece circulation guiding structure is represented by U.S. Pat. No. 6524003, wherein a tubular structure is formed by coupling two semi-circular tube parts using a plastic injection molding process. That method substantially reduces the problem of shrinking deformation, as that is significant in the one piece structure of type 1. However, there arises the extra problems of shrinking deformation caused by its slim and elongated structure; difficulty in coupling two semi-circular tube parts to each other and then precisely mating with the tunnel path formed in the sliding block. Besides, the problem of unprofitably large contact area existing between the rolling member and its guiding structure enclosing around it still can not be solved to improve the circulation of the rolling member.
The third type of circulation guiding structure, which is analogous to the second one, is structured to enclose only half the portion of the rolling member as that disclosed by U.S. Pat. No. 6203199, in which the upper and the lower walls are used to control the motion of the rolling member. The structure is also created by using the plastic molding process, which being similar to aforesaid two types, can not be free from the problems of shrinking deformation and an ineligible frictional resistance caused by a large contact area as that described in the former two types of structure. The dimensional deviation caused by shrinking deformation may lead to retardation of the rolling member by the circulation guiding structure and, in the worst case scenario, the function of the linear transmission mechanism may be completely blocked.
For these reasons the inventor has put forth every effort for years by continuous research to palliate the inherent shortcomings of the conventional techniques described above, and at last has succeeded in realizing the present invention.